Static AC/AC thyristor converter for a self-driven synchronous motor

Abstract

The invention comes within the field of static converters. A static converter which comprises two Graetz rectifier bridges connected together at their DC terminals by first and second connections. One of the bridges is connected to the AC mains by means of a transformer and the other is connected to a variable speed synchronous machine. A third connection links the neutral conductor of the stator winding of the synchronous machine to the neutral conductor of the secondary winding of the transformer. Control means of the rectifier connected to the mains provide independent control for the upper half-bridge and the lower half-bridge of the rectifier.

What is claimed is: 
     
       1. A static AC/AC thyristor converter comprising: a Graetz rectifier "machine" bridge for connection on its AC side to a variable-speed synchronous machine having a star-wound stator, and connected on its DC side via first and second conductors to a static AC/DC "mains" bridge converter for connection to three-phase AC mains, said bridges including respectively means for controlling the firing of their thyristors, said means for controlling the mains bridge converter including means for applying to said first and second conductors voltages whose polarities may be identical to each other or opposite to each other, said AC/AC converter further including a third connection having a first end connected to the center of the star winding of the stator of the synchronous machine and having a second end connected to an AC point of said mains bridge such that the current which flows in one or other of said first and second conductors when the polarities applied thereto in operation, are identical, returns to the three-phase AC mains via third connection. 
     
     
       2. A static AC/AC converter according to claim 1, wherein the static AC/DC mains bridge converter is a single Graetz rectifier bridge and is connected to the three-phase AC mains, via a transformer which includes a star secondary winding to whose centre the said second end of the third connection is connected. 
     
     
       3. A static AC/AC converter according to claim 1, wherein the static AC/DC mains bridge converter is constituted by two Graetz rectifier bridges connected together in series and wherein the second end of the third connection is connected to the point constituting the the series connection of the two bridges. 
     
     
       4. A static converter according to claim 1, wherein an induction coil is inserted in the third connection.